Abstract
Nanocrystalline HfO2:Al2O3 mixture films and nanolaminates were grown by atomic layer deposition at 350°C from metal chloride precursors and water. Formation of metastable HfO2 polymorphs versus monoclinic phase was affected by the relative amount and thickness of constituent oxide layers. The films exhibited saturative magnetization and charge polarization in externally applied fields at room temperature. The films also demonstrated resistive switching behavior with considerable window between low and high resistance states.
Highlights
Two distinctive resistance states were observed in the current-voltage loops of the nanolaminate films as characteristic of resistive switching memory materials
The magnetoelectric properties were recognized at room temperature and most clearly in the well-defined nanolaminate film
In this nanolaminate, the metastable polymorphs of HfO2 dominated the phase composition
Summary
To cite this article: Kaupo Kukli et al 2018 ECS J. Cubic and tetragonal polymorphs of HfO2 knowingly possess higher dielectric permittivity compared to that of monoclinic phase,[21] and have been attractive for applications in capacitive memory devices and electronic switches.[22] The orthorhombic phase may be considered as an interesting one in terms of electrical charge polarization, since, due to its noncentrosymmetric lattice, it could be responsible for the ability of the material to nonlinearly and saturatively polarize in external electric field. Resistive switching possibly affecting electrical control of ferromagnetism in Ag/HfO2/Nb:SrTiO3/Ag stacks has been reported.[29] Coexistence of electric field controlled ferromagnetism and resistive switching in transition metal oxide films has been recorded at room temperature earlier in TiO2 based stacks.[30] Switching currents were measured in atomic layer deposited, presumably ferroelectric, Hf0.5Zr0.5O2 thin films.[31] simultaneous evaluation of magnetization behavior, electrical polarization and switching resistivity effects in the same solid films appear justified. 31 × [15 × HfO2 + 4 × Al2O3] + 15 × HfO2 33 × [15 × HfO2 + 3 × Al2O3] + 15 × HfO2 34 × [15 × HfO2 + 2 × Al2O3] + 15 × HfO2 11 × [50 × HfO2 + 5 × Al2O3] + 50 × HfO2 35 × [15 × HfO2 + 1 × Al2O3] + 15 × HfO2 4 × [150 × HfO2 + 10 × Al2O3] + 150 × HfO2 4 × [170 × HfO2 + 10 × Al2O3] + 170 × HfO2 5 × [100 × HfO2 + 5 × Al2O3] + 100 × HfO2 5 × [120 × HfO2 + 6 × Al2O3] + 120 × HfO2 3 × [200 × HfO2 + 10 × Al2O3] + 200 × HfO2 3 × [150 × HfO2 + 5 × Al2O3] + 150 × HfO2 6 × [100 × HfO2 + 2 × Al2O3] + 100 × HfO2 2 × [300 × HfO2 + 5 × Al2O3] + 300 × HfO2 6 × [100 × HfO2 + 1 × Al2O3] + 100 × HfO2 700 × HfO2, reference film d,nm
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